Coil tempering - annealing the coil without hotspots

Coil tempering refers to a controlled heat treatment in which you briefly heat the wire with electricity after winding it, without any cotton or e-liquid being involved. The wire – typically Kanthal A1, Nichrome or SS316L stainless steel – reacts with atmospheric oxygen, forming a thin, stable oxide layer on the surface. This oxidation on the coil is exactly the effect you want: it increases the surface resistance between the individual windings, prevents unwanted short circuits between adjacent coils and ensures that the heat spreads evenly from the inside out.

The method is often described using terms such as ‘annealing the coil’ or ‘pre-heating the wire’. It always means the same thing: you heat the wire to a faint red glow, check the evenness and correct any problem areas before the cotton and e-liquid come into play.

Coil heat treatment always follows the same pattern, regardless of whether you’re using a simple round wire or a more complex fused Clapton.

Step by step

1. Insert and secure the coil: Screw the coil into the posts of your RDA or RTA. Ensure good contact and a secure fit.
2. Check resistance: Measure the resistance on the mod or using an ohmmeter (e.g. 0.4 Ω for a single coil at a moderate 25–40 W). Values below 0.1 Ω or erratic readings indicate a short circuit.
3. Pulse briefly: Press the fire button in short bursts of 1–2 seconds. The coil should glow a faint red from the inside out.
4. Correct hotspots: Between pulses, gently press any brightly glowing spots together using ceramic tweezers so that the windings heat up evenly.
5. Repeat until the entire coil becomes uniform and darker. A dull grey tone indicates that the oxide layer has formed.

Typical applications

Annealing is worthwhile for all hand-wound coils, particularly for complex windings such as Clapton, Alien or Staggered Fused Clapton. Annealing is not necessary for ready-made replacement coils for sub-ohm tanks, as these are factory-treated.

Not every wire behaves in the same way, and the wrong technique can weaken the build or shorten its lifespan. You should bear the following points in mind:

• Consider the choice of material: Kanthal and Nichrome can be annealed without any problems. SS316L stainless steel must not be annealed in temperature control mode, as this distorts the TC value. Only use SS in wattage mode if you wish to anneal.
• Short bursts rather than continuous firing: Press in 1–2-second bursts and allow the coil to cool down in between. Long periods of continuous firing overheat the wire and make it brittle.
• Consistently iron out hotspots: A coil that heats unevenly will later lead to burnt cotton and dry hits. Take your time until the coil heats evenly from the inside out.
• Safe battery: Use only intact, high-current-capacity batteries (e.g. 20–30 A continuous current) and a regulated mod with short-circuit protection. Use mechanical mods only if you have the relevant experience and have measured the resistance beforehand.
• Use ceramic tweezers: Metal tweezers conduct electricity and can cause a short circuit. Ceramic tweezers are standard when building coils.
• Measure resistance multiple times: After each burn-in process, it is worth checking the resistance again to detect any changes caused by deformation.

Do I need to temper every coil?

Hand-wound coils: yes; pre-made factory coils: no. For DIY coil builders, the oxide layer ensures consistent heating behaviour. Pre-made coils from the shop are already pre-treated and simply need to be installed.

How can I tell if the oxidation is sufficient?

After several pulses, the coil takes on a matt grey to dark hue and glows evenly from the inside out when fired again. Bright, isolated glowing spots mean that further adjustments are needed.

Can I temper stainless steel wire?

Yes, but only if you subsequently operate the coil in Watt mode. In Temperature Control mode, the oxide layer distorts the reference resistance and leads to inaccurate temperature control.

What should I do if the coil is too loose after tempering?

Carefully pull the coil tighter using ceramic tweezers and pulse again. If the coils remain uneven, it is worth rewinding the coil rather than continuing to adjust it.

When properly seasoned, a self-built coil delivers consistent heat, a clean flavour and a longer lifespan for the cotton. Seasoning becomes routine once you’ve done the pulsing and adjusting a few times – and it’s worth doing with every new build. If you prefer ready-made solutions or need a replacement for your sub-ohm tank, you’ll find suitable models in our selection of coils and atomiser heads. To get started with DIY coil-building, it’s also worth taking a look at the right accessories, such as ceramic tweezers and winding mandrels.